Add some unit tests

[xyang16]

Description

Brief description of what this PR is about

Add some unit tests

[codecov-commenter]

Codecov Report

Base: 72.08% // Head: 70.08% // Decreases project coverage by -2.00% ⚠️

Coverage data is based on head (c2f090b) compared to base (bb5073f).
Patch coverage: 70.69% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2063      +/-   ##
============================================
- Coverage     72.08%   70.08%   -2.01%     
- Complexity     5126     6035     +909     
============================================
  Files           473      600     +127     
  Lines         21970    26575    +4605     
  Branches       2351     2890     +539     
============================================
+ Hits          15838    18625    +2787     
- Misses         4925     6547    +1622     
- Partials       1207     1403     +196     

Impacted Files	Coverage Δ
api/src/main/java/ai/djl/modality/cv/Image.java	69.23% <ø> (-4.11%)	⬇️
...rc/main/java/ai/djl/modality/cv/MultiBoxPrior.java	76.00% <ø> (ø)
...rc/main/java/ai/djl/modality/cv/output/Joints.java	71.42% <ø> (ø)
.../main/java/ai/djl/modality/cv/output/Landmark.java	100.00% <ø> (ø)
...main/java/ai/djl/modality/cv/output/Rectangle.java	72.41% <0.00%> (ø)
...i/djl/modality/cv/translator/BigGANTranslator.java	21.42% <0.00%> (-5.24%)	⬇️
.../cv/translator/SemanticSegmentationTranslator.java	0.00% <0.00%> (ø)
.../ai/djl/modality/cv/translator/YoloTranslator.java	27.77% <0.00%> (+18.95%)	⬆️
...modality/cv/translator/wrapper/FileTranslator.java	44.44% <ø> (ø)
...y/cv/translator/wrapper/InputStreamTranslator.java	44.44% <ø> (ø)
... and 519 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.